Amplifier arrangements are used in a number of areas of electronics such as, for example, communications technology and industrial electronics. An amplifier arrangement may be produced as an individual integrated circuit. An amplifier arrangement may also be realized together with further circuit modules on an extensive integrated circuit, however.
FIGS. 1A to 1D show customary amplifier arrangements in accordance with the principle of the inverting amplifier. Functionally or operatively identical structural elements bear identical reference symbols.
FIG. 1A shows an amplifier 1 having a first input 4, a second input 5 and an output 6. The first input 4 is embodied as a noninverting input and the second input 5 is embodied as an inverting input. The amplifier 1 is connected to a supply voltage terminal 9 and a reference potential terminal 8 for provision of a supply voltage UC. The output 6 of the amplifier 1 thus drives a voltage that is a function of the difference between a voltage at the first input 4 and a voltage at the second input 5.
The output 6 is connected to the second input 5 of the amplifier 1 by means of a feedback resistor 31. An input 12 of the amplifier arrangement is connected to the second input 5 of the amplifier 1 via an input resistor 30. The input 12 of the amplifier arrangement serves for feeding in an input voltage UIN to be amplified. The output 6 of the amplifier 1 is connected to an output 13 of the amplifier arrangement for outputting an output voltage UOUT. The first input 4 of the amplifier 1 is connected to the reference potential terminal 8.
The gain factor G of the inverting amplifier depends on the ratio of the value of the input resistor 30 to the value of the feedback resistor 31. The gain factor G can be calculated approximately from the following equation:
      G    =                            U          OUT                          U                      I            ⁢                                                  ⁢            N                              =              -                              R            31                                R            30                                ,where UIN is the input voltage, UOUT is the output voltage, R30 is the value of the input resistor 30 and R31 is the value of the feedback resistor 31.
FIG. 1B shows an amplifier arrangement which largely corresponds to the amplifier arrangement of FIG. 1A. Instead of the feedback resistor 31 in the amplifier arrangement in accordance with FIG. 1A, in the amplifier arrangement in accordance with FIG. 1B four feedback resistors 32, 33, 65, 66 are connected in series between the output 6 of the amplifier 1 and the second input 5 of the amplifier 1.
The input resistor 30 and the four feedback resistors 32, 33, 65, 66 have the same nominal value. Therefore, the gain factor G of the amplifier arrangement in accordance with FIG. 1B is approximately −4.
FIG. 1C shows an amplifier arrangement which is constructed in a development of the amplifier arrangement in FIG. 1B. A resistor network connects the output 6 of the amplifier 1 to the second input 5 of the amplifier 1 and comprises four feedback resistors 34, 35, 36, 37 connected in series. A first terminal of the feedback resistor 34 is connected to the second input 5 of the amplifier 1 via a switch S31. A node formed between the feedback resistor 34 and the feedback resistor 35 is connected to the second input 5 of the amplifier 1 via a switch S32. Likewise, a node between the feedback resistor 35 and the feedback resistor 36 and a node between the feedback resistor 36 and the feedback resistor 37 are connected to the second input 5 of the amplifier 1 by means of a respective switch S33, S34.
If the switch S34 is closed, then the magnitude of the gain factor G is the ratio of the value of the feedback resistor 37 to the value of the input resistor 30. A gain factor G of maximum magnitude can be set in the amplifier arrangement in accordance with FIG. 1C if the switch S31 is closed and the three switches S32, S33, S34 are open.
FIG. 1D shows an amplifier arrangement which is constructed in a development of the amplifier arrangement in accordance with FIG. 1C. Eight resistors having the same nominal value as the input resistor 30 are provided as feedback resistors 38, 39, 40, 41, 42, 43, 44, 45.
As a result of the switch S34 being closed, the gain factor G can be set approximately to a value of −1. As a result of the switch S33 being closed, the gain factor G can be set approximately to −2; as a result of the switch S32 being closed, the gain factor G can be set approximately to −4; and as a result of the switch S31 being closed the gain factor G can be set approximately to −8.
The absolute values of resistors having different nominal values may be subject to great fluctuations on account of diverse influences, particularly during production in integrated circuit technology. It can happen, therefore, that in the amplifier arrangements in accordance with FIGS. 1A and 1C, the gain factor can be set only with limited accuracy on account of the great variation of the values of the resistors.
Since the resistors have the same nominal value in the amplifier arrangements in accordance with FIGS. 1B and 1D, the factors responsible for the fluctuations are reduced and a higher accuracy of the gain factor G is to be expected. An area requirement for the realization of the multiplicity of resistors may be high, however, in the amplifier arrangements in accordance with FIGS. 1B and 1D.
An amplifier arrangement should enable an accurate setting of the gain factor and an area-saving realization of the amplifier arrangement. A method for amplifying a voltage should provide an amplified voltage having a gain factor that can be set.